One notable application of string theory is the anti-de Sitter/conformal field theory (AdS/CFT) [1]}, [2]}, [3]}, [4]}, [5]} or holographic duality, which is used to study the coupling regime of quantum field theories.
This theory is also called gravity/gauge duality. This principle is based on closed and open string duality according to the relationship between the open and closed strings. As such, in this principle, the gravitational field corresponding to the closed string is defined by the boundary and the field theory corresponding to the open string by the bulk of the AdS space. QGP (Quark Gluon Plasma), condensed matter systems, and other QCD problems which is impossible to solve by helping perturbative theory have been investigated using this duality. The duality between gravitational and gauge theories is the strong-weak duality, which also was adapted to describe the low- and high-energy dynamics of Quantum Chromodynamics. It is also important to investigate hadron interaction processes in the nuclear medium in a proton-proton and heavy ion collisions in order to study phase transition of QGP and evolution of the early Universe.
